Referring now to background FIG. 1, trees 101A-101B are often planted near sidewalk 100 to provide aesthetics and shade from sunlight. Large trees, especially evergreens and shade trees, such as ficus, are popular with city planners because of their hardiness and year round appeal. Unfortunately trees may have extensive roots systems that over time may displace or even crack sidewalk tiles.
Each tree 101A-101B may have one or more roots 102A-102B that may spread out from the original position where the trees were planted. Sometimes these roots go under sidewalks and force the sidewalk upward thereby cracking it so that it requires repair as illustrated by the cracks 105A-105D. The cracks may become so large over time that the broken sidewalk 100A-100D not only becomes an eyesore but a hazard to pedestrians walking over it, possibly tripping a pedestrian to fall onto the sidewalk 100.
Traditionally formed sidewalk has vertical sides. Moreover, expansion joints may be small or non-existent so they are not easily displaced or moved upward by tree root systems. As a result traditionally formed sidewalk is more likely to crack and be damaged from tree roots. The vertical sides present a relatively large surface area which closely abuts the neighboring tile leaving little or no gap between. A high friction coefficient of concrete resists abutting sides of sidewalk from sliding against each other. As pressure from the roots increases, traditionally formed tiles of sidewalk may crack before they are displaced as illustrated by the cracks 105A-105D in sidewalk tiles 100A-100D. Even if they don't crack, displaced tiles still present a hazard to a pedestrian. Lifted edges of a sidewalk tile may trip up a pedestrian leading to an annoying if not painful tumble.
Each city may be in charge of repairing a broken sidewalk. Once cracks form or the tiles are displaced, city contractors may grind uplifted cracks or patch the cracks with asphalt. However if the cracks are unrepairable, city contractors may generally demolish the offending sidewalk tile. The broken sidewalk is cut away and demolished into rubble so that it can be hauled away.
With the sidewalk removed, the exposed tree roots that cause the damage can be cut away from the tree from the surface below the sidewalk. The soil underneath the sidewalk can be re-graded. A frame of lumber (often two-by fours cut and hammered together with nails) is built around the exposed soil where new sidewalk tile is to be formed. New concrete is poured into the wooden frame to form a new slab of concrete to replace the broken portion of the sidewalk. Depending on the weather concrete may take 3-7 days to cure properly, during which time the sidewalk may be roped off to avoid use.
After sufficient curing time to form concrete sidewalk, the city contractors return to the site and remove the wooden frame and barricades. Landscaping may also be performed to restore the area into having a more esthetic look.
Cities may have hundreds of miles of sidewalks with trees periodically planted next to it. Traditional repair of sidewalks may be costly for a city and its tax paying citizens if there are numerous miles of tree-line sidewalks. Reduction in material and labor time costs to repair sidewalks may save considerable sums of money for a city with numerous miles of tree-lined sidewalks.